Asynchronous Video: Coordinated Video Coding and Transport for Heterogeneous Networks with Wireless Access

Abstract

Wireless access to continuous-media services such as video, voice, and audio is becoming increasingly prevalent. Interactive video services such as video conferencing and multimedia editing are two such services of particular interest. We discuss some of the problems with using the MPEG standard (which was designed for wired, circuit-switched services) for wireless packet-video transport in a mobile environment. We propose a novel strategy for video transport using a layered source coder in conjunction with a variable QOS, multiple-substream abstraction for the transport. This abstraction addresses specifically the need to obtain simultaneously high spectral efficiency, good subjective quality, and low perceptual delay on a wireless channel. It also addresses the heterogeneous transport resulting from the concatenation of a wireless access link with a broad-band backbone network.

We use asynchronous video (ASV) reconstruction, running counter to current techniques, which use strictly synchronous (frame-by-frame) video processing. By doing so, we hope to achieve a perceptual delay that is much lower than the worst-case transport delay. By perceptual delay, we refer to the effective end-to-end latency observed by the user, for example as represented by the audio delay required to maintain lip synchronization. By identifying packets to the transport with relaxed reliability and/or delay requirements, the transport (particularly wireless) can achieve high traffic capacity. Reasonable and promising simulation results are achieved, although much work remains on achieving significant video compression in this environment.